Reduced engine operation times in hybrid vehicles enable fuel economy and reduced fuel emissions benefits. However, the shorter engine operation times can lead to insufficient time for completion of various on-board diagnostic operations. These may include, for example, fuel system leak diagnostics, diagnostics for various engine sensors, etc.
One example approach to enable completion of on-board diagnostic routines involves maintaining or resuming engine operation for a duration to complete the routines. Another example approach is shown by Matsuoka et al. in U.S. Pat. No. 6,446,61 wherein an engine is held in a steady-state during engine operation so that a canister leak detection monitor can run.
However, the inventors herein have identified potential issues with such approaches. As an example, operating an engine to complete diagnostic routines may reduce fuel economy. As another example, holding an engine in a steady state to complete a leak detection may reduce a number of diagnostics that need to be completed, but not sufficiently. For example, even with the leak test completed during engine operation, the engine may need to be restarted at a later time to complete other diagnostics over a drive cycle. As such, these repeated intrusive engine operations may dissatisfy the vehicle operator. Specifically, a vehicle operator wanting to drive a hybrid vehicle in an electric mode may be dissatisfied with repeated engine operations that were not in response to an operator torque request.
In one example, some of the above issues may be addressed by a method for operating a hybrid vehicle comprising: performing a first set of diagnostic routines during steady engine conditions; performing a second different set of diagnostic routines during non-steady engine conditions; and during engine running following a first engine hot-start of a vehicle drive cycle, holding the engine steady in response to a total number of incomplete diagnostic routines in the first set. In this way, an accuracy and completion of on-board diagnostic routines is improved.
As an example, a control system of a hybrid vehicle may need to complete a variety of on-board diagnostic routines over a drive cycle for emissions compliance. The variety of on-board diagnostic routines may include a first set of routines that are (stringently) performed during steady engine operating conditions and a second set of routines that are performed during non-steady operating conditions. One or more of the diagnostic routines from either set may be opportunistically performed during a vehicle drive cycle as vehicle conditions shift from an electric mode of operation to an engine mode of operation and between engine steady and non-steady conditions. A controller may monitor a total number of diagnostic routines in each set that are completed as well as a number of those diagnostic routines that are enabled (that is, ready to be completed once the appropriate engine conditions are present).
During engine running following a first engine hot start of a vehicle drive cycle (that is, immediately following and contiguous with the engine running of the hot restart with no stops in between), in response to a ratio of the number of diagnostic routines of the first set that are incomplete and enabled relative to the total number of incomplete diagnostic routines of the first set being higher than a threshold, a controller may intrusively hold an engine steady for a duration. In particular, during a first engine start from rest where an engine temperature is above a threshold (that is, the engine has warmed up), an exhaust catalyst temperature is above a threshold (that is, an exhaust catalyst is sufficiently hot) and while the vehicle is travelling below a threshold altitude, the controller may hold an engine speed and load held within a threshold range, for a duration, irrespective of an operator torque demand over the duration. That is, the engine may be held steady with low variation in engine speed and load so that steady conditions are actively provided for completing the enabled and incomplete diagnostic routines of the first set. In the interim, an operator torque demand may be met by a system battery.
In this way, diagnostic routines requiring engine steady conditions can be completed during a drive cycle of a hybrid vehicle with reduced engine-on times. By holding the engine steady to complete the diagnostic routines only if a sufficient number of diagnostic routines are incomplete and enabled, repeated engine operation for completion of the routines is reduced. By completing the required set of diagnostic routines within a drive cycle, emissions compliance is improved. In addition, by holding the engine steady in a forced steady mode for diagnostic routines requiring stringent engine steady conditions, an accuracy and integrity of the results are improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.